This invention relates to a process for ex-situ presulfurization of generally porous particles of hydrocarbon hydroconversion catalysts. The invention also relates to processes for ex-situ presulfurization of porous particles of hydrotreatment catalysts, followed by in-situ or ex-situ activation of the catalysts that are thus sulfurized by a reducing compound, particularly a gas that contains hydrogen. The invention also relates to the use of catalysts that are thus presulfurized and optionally activated for the hydroconversion of hydrocarbon feedstocks.
Hydroconversion catalysts are widely used in industry, for example for hydrodesulfurization and/or hydrodenitrogenation and/or hydrodemetallization of hydrocarbon feedstocks that contain sulfurous, nitrogenous, and/or metal impurities. They are also commonly used in cases where the feedstock contains unsaturated components that should be saturated: here again, the hydrotreatment catalysts provide a solution. These processes are also called hydrotreatment processes. It is also common practice to use hydrocracking hydrocarbon feedstocks. Knowing what process will be carried out in actuality and to what extent depends on the conditions selected (feedstock, catalyst, pressure, temperature, etc.). In all these processes, the feedstock is brought into contact with the hydrogen-containing gas within a reactor, under conditions that comprise high pressure and high temperature.
The hydroconversion catalysts are well-known to one skilled in the art. They contain hydrogenation metals that are placed on a substrate that may or may not be amorphous or zeolitic, or mixtures of these substrates.
The metals that are commonly used are cobalt, nickel, molybdenum, and tungsten, generally in combination, particularly the cobalt/molybdenum, nickel/molybdenum, cobalt/tungsten and nickel/tungsten combinations. The hydrotreatment catalysts may also contain noble metals, for example, platinum, palladium and/or rhenium.
The substances that are most frequently used as substrates are alumina, silica, silica/alumina, and magnesium. The substrate can also consist of or contain a zeolite, for example a zeolite such as Y. Normally, when zeolites are used, they are used in combination with one or more of the other above-mentioned substances that are used as a substrate.
After the preparation of the catalyst, the hydrogenation metals are generally in oxidized form. This also applies to used catalysts that have undergone regeneration treatment.
It has been known for a long time that the metals should be in the form of their sulfides to obtain optimal results. The metal oxides (or the metals themselves in the case of zero-valence metals) should therefore be converted into corresponding sulfides.
This sulfurization is traditionally carried out in-situ, i.e., within the reactor in which the catalyst is to be used, generally by bringing the catalytic particles into contact, in the reactor and at an increasing temperature, with a combination a hydrogen-containing gas and hydrogen sulfide or a combination of hydrogen-containing gas and a hydrocarbon flow that is often diluted with a sulfurated compound.
Developments have occurred over the last ten to fifteen years, wherein specialized companies now supply the catalyst with the amount of sulfur or sulfurated compound that is required for the final ex-situ sulfurization, i.e., outside the treatment reactor, generally at another site; this process is called ex-situ presulfurization. One of the advantages of such ex-situ presulfurization lies in the fact that the refiner who acquires the catalyst can proceed with activation in a relatively easy manner; to obtain the desired formation of metal sulfides, all the refiner has to do is treat the catalyst with a hydrogen-containing gas within the treatment reactor. The other main advantages of this process lie in the fact that it reduces the down time of the reactor and that it allows the refiner to avoid using toxic chemical products such as hydrogen sulfide and mercaptans.
Several ex-situ presulfurization methods developed over the last few years use elemental sulfur. These methods are described in, among other things, U.S. Pat. Nos. 4,943,547 and 5,215,954. The methods that are described in U.S. Pat. No. 4,943,547 comprise bringing the elemental sulfur into contact with the catalytic particles that are to be presulfurized, either in the form of powdered sulfur, which is then sublimated in the pores of the catalyst, with the mixture that is obtained then being wetted with a high-boiling oil or a hydrocarbon solvent, or in the form of a suspension that was previously prepared from elemental sulfur in a high-boiling or a hydrocarbon solvent. In U.S. Pat. No. 5,215,954, which follows up on U.S. Pat. No. 4,943,547, a liquid olefin is used instead of a high-boiling oil or a hydrocarbon solvent. In all these methods, the catalytic particles are brought into contact with elemental sulfur into the pores of the catalyst by sublimination or by melting requires accurate monitoring of the conditions of the process, which is difficult to ensure.
An object of this invention is to mitigate these difficulties.